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Compound bucket study

Compound bucket study. Recycler Meeting May 2, 2007 A. Shemyakin, C. Bhat, , D. Broemmelsiek, M. Hu. Motivation. We are not using the full strength of e-cooling, keeping the e-beam far off axis most of the time, because of life time degradation

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Compound bucket study

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  1. Compound bucket study Recycler Meeting May 2, 2007 A. Shemyakin, C. Bhat, , D. Broemmelsiek, M. Hu

  2. Motivation • We are not using the full strength of e-cooling, keeping the e-beam far off axis most of the time, because of life time degradation • We need the stochastic cooling only to cool tails, and it becomes too weak at large intensities • The idea: to separate in space the tails and the core • E-cool holds the core and creates a correlation between the longitudinal and transverse tails • Tails are cooled by a high-gain transverse stochastic cooling outside the core • The hope was that pbars with a high transverse action would be heated by IBS longitudinally fast enough to go to the tail (hot) area before being lost transversely

  3. Tails correlation in e-cooled beam- interpretation • Two reasons for the poor e-cooling of the transverse tails: • Tail pbars spend less time inside the electron beam • Increased transverse pbar velocities inside the e-beam Measured radial dependence of the drag rate (20 & 24 Feb 2006, L.Prost). A simple model of a drag force vs action: Force = [average of the measured F(r) over phases] * e2/(e2 + p2) A side note: we have to try increasing the effective e-beam size.

  4. Cooling of longitudinal and transverse tails • All with small transverse action pbars captured inside the bucket are cooled • The drag force drops by ~ 3 times at 20 MeV/c • The drag force drops by ~10 times for pbars with action ~10 , which are still far from being lost (RR acceptance ~40)

  5. Tails correlation in e-cooled beam Longitudinal Schottky profiles in the time of scraping (L. Prost, 31-Mar-07). Green- before scraping, 11.E10; Red- after the horizontal scrape, 7.E10; Yellow- after vertical scrape, 3.E10. In the time of transverse scraping, the longitudinal momentum spread of an e-cooled beam decreases dramatically. The effect depends on how long the electron cooling has been applied. No similar data for a stochastically-cooled beam were found.

  6. The study (24-Apr-07) – RF structure RF and RWM (15:03) profiles. (1)-entire beam, (2)- cold area, 165 bckt; (3)- hot area, 192 bckt. Main burrier length = 48, mini-barriers = 13 bckt. 3 2 1

  7. The study history • Immediately after the transfer, the pbar beam was moved into a desired longitudinal position and set to the desired length • Np ~ 250 E10 • Before growing the mini-buckets: • dPsig = 5.3 MeV/c • FW = 5.3  • Transv. Schottky emittance = 6.8  • 13-bckt-width, full-amplitude mini-buckets were grown • The width of the cold bucket (165 bckt) was chosen to fit inside the standard bucket squeezed for a transfer of 4 batches • At the same time, e-beam was turned on (0.1 A, on axis) • Transverse stochastic cooling was gated to outside of the cold beam • Longitudinal cooling was off • Turning on and initial tuning took for about an hour • Was adjusted once more an hour later • ~ 3 hours after raising mini-buckets, the stochastic cooling was turned off • In less than an hour after, the mini-buckets were removed, and normal operation resumed

  8. Density distribution and life time New parameters (P. Derwent): integrals over RWM distribution for three areas: (1)- entire beam, RWMD67; (2)- cold, RWMD47, (3)- hot, RWMD47 Portion of the beam in the cold area R:RWMD67 R:BEAM • Portion of the beam in the hot area dropped from 35 to 5% • Intensity reported by R:BEAM was changing up to 3% (difficult to interpret) • The life time estimated by RWMD47 stayed ~700 hr for the first ~2 hours after turning e-beam on, but dropped to ~150 hr after that. SC power

  9. Transverse emittances • The cold area portion behaved as it usually does for the case of e-cooling only • FW emittances were steadily decreasing, while Schottky emittances remained nearly constant. • The hot portion behaved as it usually does for the case of stochastic cooling only • FW and Schottky emittances were close • Cooling rate 2.3 /hr for (50- 20)E10 • Schottky emittance grew fast after turning stochastic cooling off • Indication of a flow from the cold area? Indexes 1,2, and 3 corresponds to the entire beam, cold, and hot areas. Averages of H and V are shown.

  10. Cooling by e-beam only • After turning the stochastic cooling off: • The number of pbars in the hot area stopped decreasing • The total transverse Schottky power stopped decreasing

  11. Longitudinal Schottky data RMS Schottky momentum spread measured in cold (2) and hot (3) areas as well as ungated data (1). See A. Burov’s talk for the analysis of the longitudinal dynamics.

  12. Summary • No major discrepancies with qualitative models were found • 95% of the beam was cooled into the cold bucket • Gated stochastic cooling worked • A strong tail correlation in an e-cooled pbar beam fits into observations • There was an indication of a flow of high-action particles from the core to the tail area • Cooling was not faster than normal • In 4 hours with mini-buckets, changes in emittances were • From 133 to 48 eVs • From 6.9 to 5.7  Schottky • From 5.3 to 2.4  FW • Optimum stochastic cooling was applied for 2 hrs only • The hot area can be expanded • There were indications of the life time degradation toward the end of the study • Usual trend for e-cooling with e-beam on axis • Agrees with a nearly constant transverse Schottky emittance of the cold area • An explanation is a too slow rate of moving the high– action pbars into the hot area

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